Threaded joints are widely used in connecting pipes for use in oil and gas production, such as oil well pipes. For the connection of pipes for use in oil or gas prospecting and production, standard threaded joints based on the American Petroleum Institute (API) standard are conventionally used. However, since crude oil wells and natural gas wells have recently increased in depth, and horizontal wells and directional wells are now more common than vertical wells, excavation and production environments are increasingly under harsh condition. Furthermore, an increase in well development under hostile environments, such as in ocean and polar regions has led to diversified performance requirements for threaded joints, such as compression resistance, bending resistance, and external pressure resistance. This therefore increases the use of high-performance special threaded joints called premium joints.
The premium joint is generally a joint composed of a pin component and a box component joined together, each including a tapered thread, a seal (specifically, a metal-to-metal seal), and a shoulder (specifically, a torque shoulder). The tapered thread has a key role in firmly securing the tubular joint, the seal ensures sealability due to the box component and the pin component coming into metal-contact at this portion, and the shoulder serves as a bearing face that acts as an abutment during the make-up of the joint.
FIGS. 2 to 4 are schematic explanatory diagrams of a premium joint for an oil well pipe, which are vertical cross-sectional views of a cylindrical threaded joint. The threaded joint includes a pin component 3 and a box component 1 corresponding thereto. The pin component 3 (pin 3) has a male member 7 at its outer surface and a no-threaded portion called a nose 8 (pin nose 8) at an end of the pin 3, which is provided next to the male member 7. The nose 8 has a seal 11 at the outer peripheral surface thereof and a torque shoulder 12 at the end face thereof. The opposing box component 1 has a female member 5, a seal 13, and a shoulder 14 at the inner surface, which are portions that can be screwed on or come into contact with the male member 7, the seal 11, and the shoulder 12 of the pin 3, respectively.
Examples of the related art of the foregoing premium joint are disclosed in Patent Literatures 1 to 6.